FIG. 3 is a schematic configuration diagram illustrating one example of a conventionally-known general liquid chromatograph mass spectrometer (LC/MS). A sample liquid temporally separated and eluted from a column 11 of a liquid chromatograph section (LC section) 10 is introduced into an interface section (atmospheric pressure ionization interface) 20, and is then sprayed from a spray nozzle 22 into an ionization chamber 21 to be ionized. Fine droplets including ions generated go inside a tubule (desolvation tube) 23 placed ahead and are sent to a mass analysis section (MS section) 30. The desolvation tube 23 is warmed by a heater (which is not shown) and the evaporation of the solvent in the droplets progresses while the solvents pass thorough inside the desolvation tube 23 to further continue the generation of the target ion.
The MS section 30 is composed of three chambers; a first intermediate chamber 31, a second intermediate chamber 32, and an analysis chamber 33. The ionization chamber 21 and the first intermediate chamber 31 communicate with each other through the desolvation tube 23. The first intermediate chamber 31 and the second intermediate chamber 32 communicate with each other through a passage hole (orifice) 36 with a small diameter placed on the top of a conical skimmer 35. Inside the ionization chamber 21, an atmosphere is maintained at approximately atmospheric pressure. The first intermediate chamber 31 is exhausted to approximately 1 Torr by a rotary pump. The second intermediate chamber 32 and the analysis chamber 33 are respectively exhausted to approximately 10−3-10−4 Torr and to approximately 10−5-10−6 Torr by a turbo molecular pump. The analysis chamber 33 is maintained in a high-vacuum state by heightening the degree of vacuum in a stepwise manner from the ionization chamber 21 to the analysis chamber 33.
The ions that have passed through the desolvation tube 23 are converged into the orifice 36 by a first ion lens 34, and pass through the orifice 36 to be introduced into the second intermediate chamber 32. The ions are then converged and accelerated by a second ion lens 37 to be sent to the analysis chamber 33. Only the target ions having a particular mass number (mass/charge) pass through the space across the long axis of a quadrupole filter 38 placed in the analysis chamber 33 and reach an ion detector 39. In the ion detector 39, a current corresponding to the number of the ions reached is taken out as a detection signal.
In the aforementioned configuration, the interface section 20 ionizes various kinds of sample components included in a sample liquid by atomizing the sample liquid by heating, high-speed gas stream, high electric field, etc. As the ionization method, an electrospray ionization (ESI) method and atmospheric pressure chemical ionization (APCI) method have been most widely used.
FIG. 4(a) illustrates a configuration example of an ionization spray section according to an ESI method. In ESI, a DC (direct current) high voltage of approximately several kV is applied to the tip portion of the spray nozzle 22 to generate a strong non-uniform electric field. The sample liquid that has reached the tip of the spray nozzle 22 is charge-separated by this electric field, and is sprayed as micro-charged droplets into the ionization chamber 21 with the assistance of a nebulizer gas blown from a nebulizer tube (not shown) placed concentrically around the spray nozzle 22. In the ionization chamber 21, a heated dry gas is supplied from a dry gas supply port 24, which is placed around the desolvation tube 23, by a heated gas supplier which is not shown. The heated dry gas is sprayed in a mist flow and the evaporation of the solvent in droplets accordingly progresses to proceed the generation of gaseous ions.
FIG. 4(b) illustrates a configuration example of an ionization spray section according to an APCI method. In the APCI method, a needle-like discharging electrode 25 is placed in front of a spray nozzle 22. A sample liquid is sprayed into a heater 26, which is placed to encircle the tip of the spray nozzle 22, by using a nebulizer gas. Consequently the solvent and the sample molecules are vaporized. The sample molecules are made to chemically react by carrier gas ions (buffer ions) generated by a corona discharge from the discharging electrode 25. Accordingly, the ionization is carried out.
In general, an APCI is effective to ionize low-polarity through middle-polarity compounds, and ESI is effective to ionize middle-polarity through high-polarity compounds. In addition, in an ESI, since multivalent ions are generated in the process of ionizing protein or other substances, it is possible to measure compounds having several tens of thousands of molecular weights, which are beyond the upper limit of the apparatus' mass range. Therefore, both ionization methods are used according to the kind of sample to be analyzed, the analytical objective, etc. Conventionally, in a general LC/MS, an ESI spray section and an APCI spray section can be easily changed; the analyst properly changes the spray section according to the ionization method. Since such changing operation causes much trouble, however, this is one of the reasons to decrease the analytical efficiency.
Given this situation, in order to save such changing labors, some conventionally-proposed apparatuses have both ionization means in the same ionization chamber. For example, Patent Document 1 and Patent Document 2 describe an ionization interface using a common spray nozzle for ESI and APCI. With these interfaces, it is possible to perform an ionization according to ESI by applying a direct current high voltage to the tip of a spray nozzle, and concurrently, it is possible to perform an ionization according to APCI by a corona discharge by a discharging electrode placed on the tip of the spray nozzle.
[Patent Document 1] U.S. Pat. No. 6,646,257
[Patent Document 2] International Publication Pamphlet No. 03/102537